Cryogenic pressure vessels and pipes for storing and transporting liquefied gases must have high strength and toughness to be able to withstand both thermal and mechanical shocks. Further, alloys with high strength and toughness are also desirable for use in extra-terrestrial applications since the sheet thickness required is reduced, thereby saving both weight and space. It should be noted that data pertaining to the strength and toughness of alloys at room temperature does not necessarily indicate the toughness behavior at lower temperatures and alloys which exhibit high strength characteristics do not necessarily possess correspondingly high toughness.
Attempts have been made in the prior art to produce a high strength, high toughness steel alloy capable of use at cryogenic temperatures. A number of examples of such attempts can be found in the patented art. For example, U.S. Pat. No. 3,838,407 (Parker et al) discloses a Fe--12Ni--0.5Ti alloy which is said to be suitable for cryogenic use and to exhibit a Charpy V-Notch toughness value up to about 170 ksi .sqroot. in. and a yield strength of about 150 ksi. Moreover, further attempts at producing high strength steel alloys for cryogenic use are disclosed in U.S. Pat. Nos. 3,132,938 (Decker et al) and 3,514,284 (Eiselstein). The former discloses a steel comprising 17 to 19% Ni, 8 to 9% Co, 2.8 to 3.5% Mo, 0.05 to 0.15% Al as well as other elements in small amounts. The latter discloses a nickel-iron alloy which comprises 36 to 42% Ni, Nb and Ta and up to 0.015% Al, with the remainder being Fe and small amounts of other elements. Other patents of interest include U.S. Pat. Nos. 3,348,981 (Goda et al) and 3,388,988 (Nagashima et al). The former discloses an alloy which is said to possess good strength characteristics at low temperatures and which comprises 0.04% to 0.17% Al together with Mn, Cr, and C. The alloy disclosed in the Nagashima et al patent is also said to to tough at low temperatures. This alloy comprises 4.5 to 7.5% Ni, together with Al, Mn, Cr, W, Mo and other elements. Also, U.S. Pat. No. 3,338,709 (Baker et al) discloses a high strength steel said to have good toughness which comprises 8 to 10% Ni, 3 to 5% Co, 0.5 to 2.5% Mo, 0.1% Al and other elements. A final patent of interest in U.S. Pat. No. 3,232,777 (Sadowski) which relates to maraging steels using high levels of chromium and molybdenum. The steels disclosed are said to be of high strength and ultra tough. In an example of interest, the steel alloy is composed of 9.5 to 13.5% Ni, 2.5 to 8Cr, 1.9 to 4.2% Mo, up to 0.75% Al, Ti, Ni and other elements in small amounts. It will be understood that the patents discussed above are exemplary only and that this listing is in no way represented to be exhaustive.